1. Field of the Invention
The present invention relates to an industrial robot provided with direct-drive motors as the driving means, especially appropriate for painting.
2. Prior Art
Recently, industrial robots are used for carrying out the various kinds of works, by executing the corresponding working programs, as machines for automatically painting, welding an the like, instead of men.
Such and industrial robot should have the body constructed in an explosion-proof manner, when it is used in a flammable atmosphere. Here, the explosion-proof manner means the manner with which the atmosphere prevents catching fire from the spark and the like, even if the electric parts of the robot produce sparks and the like. Especially, as the painting robot puts the body in the atmosphere where the flammable solvent vapors exist, the hydraulic robot is conventionally used, for the reason that the design for the explosion-proof construction is relatively simple.
However, the hydraulic robot has the disadvantages that it needs the hydraulic unit and the maintenance thereof is troublesome. Therefore, recently, an electrical robot is used as a painting robot, instead of the hydraulic robot.
Meanwhile, the above-mentioned electric robot must be provided with a plurality of electric elements, such as the motor, electric wire connected to the motor and the like, as the explosion-proof objects. For this reason, the electric robot should be constructed in an explosion-proof manner, so it has several kinds of disadvantages as follows.
In case of the robot which adopts the internal pressure explosion-proof construction as an explosion-proof manner, the scavenging gas, such as air, is blown into the space where the electric elements are arranged. And the internal pressure is increased and then the scavenging gas is exhausted from the space. Thus, at the time of use, the above-mentioned space is scavenged by the scavenging gas, so the external atmosphere is prevented from being in contact with the electric elements within the robot.
However, in the conventional robot constructed in an internal pressure explosion-proof manner, as the gas passage system thereof is complicated and the pressure loss becomes large, it takes much time to scavenge and the stagnation easily occurs in the gas flow. Therefore, a difficult problem arises that these shortcomings reduce the explosion-proof reliability.
Particularly, in case of the robot arm (the second arm), providing the wrist mechanism at the end portion, wherein the motor for driving the wrist mechanism is located, the above-mentioned problems have arisen. Because, the conventional technique cannot cause the scavenging gas to flow efficiently into the place where the motor is arranged, because the gas passage system, at the place where the motor is arranged, becomes so much complicated.
Further, the conventional electric painting robot should arrange the wires such as the power line of the motor in the narrow and complicated space within the main unit thereof, so that the assembly operation thereof must be difficult. In addition, it is difficult to wire the robot with enough room to be remained. Due to such difficulties of wiring, excess force can be easily applied to the wires when the robot moves. Therefore, the reliability of the robot becomes low because there is possibility in that the wires can be broken with ease.